The present invention relates to a guide wire having a flexible distal end for introducing a catheter to a desired part in a blood vessel of a human body for treatment or examination, such as angiography, a blood vessel occlusion technique, a vasodilation technique or the like.
A guide wire is used to introduce a catheter into a lesion site at which a conventional surgical operation is difficult to carry out, for example, percutaneous transluminal coronary angioplasty (PTCA), cardiovascular angiography, a blood vessel closing operation or the like.
Blood vessels have complicated curvatures and a guide wire is introduced to a desired part through the curved blood vessels. Therefore, a pertinent flexibility is required for a distal end of a guide wire in order to prevent damage to the blood vessels with which the introduced guide wire is brought into contact.
A guide wire usually comprises a core wire made of stainless steel or the like. Conventionally, there is frequently used as a guide wire, a so-called resin coated guide wire in which a distal section of the core wire is coated with a synthetic resin such as tetrafluoroethylene to provide smoothness to a surface of the core. In this resin coated guide wire, the distal section of the core wire is tapered to thereby provide flexibility in order to facilitate in selecting a blood vessel in which the wire is to be inserted or in reaching a desired part and preventing damage to the blood vessel.
Such tapering processing can be carried out by subjecting a straight core wire to a grinder referred to as a centerless grinder or by dipping a portion of a core wire to be a distal section in an electrolyte solution and pulling up the portion successively and slowly from the solution.
The core wire can be coated with a resin by a resin extruder. However, one tapered short core wire must be separately coated with a resin. Accordingly, a distal end of the tapered short core wire is conventionally welded to a proximal end of another tapered short core wire by a laser or an arc welder to become a certain length of wire. Thereafter, the connected wire is coated with a resin continuously and cut at the thinnest parts of the connected wire into relatively short pieces that become a core wire having both distal and proximal ends. Then there is carried out a so called rounding process in which the cut and exposed cross section of both the distal end and proximal end of the core wire are coated with a resin.
However, according to such a conventional process, joint portions of the core wire become extremely slender and when a resin is extruded onto the surface of the core wire under a constant extruding pressure, the pressure is temporarily reduced at the joint portion and an amount of extruded resin varies according to the diameter of the core wire. Therefore, there are posed problems in which a stepped outer surface is produced on the joint portions, or the joint portions become more slender than unfabricated portions, flexibility differs with each guide wire and an influence is effected on an outer diameter of a straight portion on a proximal end of the core wire.